Introduction to the antenna design of iPhoneX

The Apple 8X with full screen has attracted many purchasers. The phone behind the screen is different from the previous one. The phone starts to look a bit like art.

When Apple 6 came out, it created a record of long queue purchases, and three of the five Americans wanted to change. Now Apple's 8X full screen began to catch up with the grand occasion. It is reported that Apple will drive nearly 200 million 8X mobile phones in 2018.

The advantages of the full screen are not much to say. The following is the trouble: affecting the antenna design and how to ensure the antenna index.

Compared with the traditional screen area, the full screen occupies the traditional antenna territory: the antenna parts at the upper and lower ends of the mobile phone.

The antenna design requires a clearance area, which means that the area where the antenna is laid is free of metal. However, the full screen is equivalent to a metal layer, and the frequency band of electromagnetic radiation generated when the display piece is in operation covers the working frequency band. The efficiency of the antenna is reduced and the signal to noise ratio is also reduced.

To this end, we need to make the following efforts to protect the RF indicators:

(1) Increase the transmission power

(2) The antenna is split into 2 parts

The antenna is split into two parts, one part is to take the signal with the exposed frame section, and the other part is used for impedance transformation. The impedance transformation part is far away from the metal and interference layer.

(3) Interference of the screen

Magnetic and metal double-layer materials can be attached to the OLED screen to reduce electromagnetic radiation.

(4) Using a low-loss antenna substrate and designing a low-loss transmission line with an ultra-thin structure

In general, the commonly used fpc PI substrate (polyimide substrate) has an electromagnetic loss of 2%. In the 2.4Ghz band, it will cause 3db transmission loss, so LCP material with lower electromagnetic loss (liquid crystal polymerization) Liquid Crystal Polymer is used as a substrate to reduce signal loss.

The Apple 8X uses this LCP antenna substrate to reduce antenna loss while replacing multiple coaxial lines.

Transmission loss is a phenomenon in which an electrical signal transmitted in a circuit tends to be converted into heat and decays with the transmission distance or the resistance of the circuit itself. The degree of loss depends on the properties of the conductor (circuit) and the insulator (board material) that is in contact with the circuit. The LCP material is fabricated into a multilayer structure (metal layer, wiring layer, metal layer) instead of a coaxial cable.

The LCP film is used, and the antenna is designed on the same, and the low-loss signal is taken out to the chip end by the coplanar waveguide CPW, and the thick coaxial cable is omitted. And multiple RF lines can be taken together.

The LCP material can also be injection molded and the LDS process is used to implement the antenna function.

In short, the use of the comprehensive screen of Apple 8X guarantees that the RF index has not decreased. It is realized through material selection. It also previews two technologies of RF antenna substrate and small-frequency transmission of RF signal in the 5G era, which deserves peer attention.

Source: Blog Stereo Circuit - (Industry Information Convergence)